Title tags can have a big impact on rankings. Get the title tag right, and you can leapfrog several competitors on the 1st page of search results. We put a lot of emphasis on optimizing (and testing) the Title tag for every page on your site.
Meta descriptions don’t necessarily have a direct affect on your search engine rankings, but… well-written meta descriptions can have a huge impact on your click-through-rate (CTR), and your click-through-rate does factor into where search engines are willing to rank your site in the SERP’s.
Header tags (H1, H2, H3…) help search engines understand what a web page on your site is all about. H tags (as they’re also referred to) allow the the search crawlers to understand which content is the most important.